Treating phosphate rock to eliminate fluorine



TREATING PHOSPHATE ROCK TO ELIMINATE FLUORINE Filed Nov. 15, 1934flap/mic I Back Feeder I Harry A. C urf/s Sk M Patented June 23, 1936TREATING PHOSPHATE ROCK TO ELIMI- NATE FLUORINE Harry A. Curtis,Knoxville, Tenn; assignor to Tennessee Valley Authority, Wilson D'am,Alabama, a corporation Application November 15, 1934, Serial No. 753,137

4 Claims. (01. 71-4) (Granted under the act of March 3, 1883, as amendedApril 30, 1928; 370 0. G. 757) This application is made under. the Actof April 30, 1928, and the invention herein described, if patented, maybe manufactured and used by or for the Government for governmentalpurposes without the payment to me of any royalty thereon.

This invention relates to the process of treatment of phosphate rock.

A One of the objects of. this invention is the conversion of phosphaterock into a product in which a substantial portion of the phosphorus isin such a form as to be available for plant food. Another object of thisinvention is the removal of a substantial portion of fluorine whichoccurs in a.combined form in phosphate rock. Still another object ofthis invention is the treatment of the phosphate rock to render itsuitable for use as a stock food. Other objects of this inventioninclude the conversion of phosphate rock into a product which is a moresuitable raw ma terial for the production of phosphorus and/or 7 itscompounds.

" largely of steam with the removal of most of the combined fluorine. Nomethod has heretofore been found whereby the important factors ofgaseous atmosphere with high partial pressure of water vapor andtcmperaturemay be adequately controlled to obtain economical conversionof the phosphate rock into available" form. v

I have found that, by passing fine granular.

phosphate rock thru a suitable apparatus continuously andcountercurrently to a stream of gas consisting essentially of steamproduced by the direct combustion of hydrogen and oxygen, a

product of high plant food availability is obtained. The-thermalrequirements of the process be reduced by circulating a part of thesteam thru the apparatus in a suitable manner.

A diagrammatic vertical section of one form of apparatus for theembodiment of my process is shownin the accompanying drawing. Thecharging means l, is arranged to supply fine granular. phosphate rock'continuously to the thermally insulated and refractory lined furnace Thephosphate rock is heated bythe combastion of hydrogen and oxygensupplied to a plurality of burners located about the midsection ofthefurnace of which burner 3, is representative. Each of these burners issupplied by.

hydrogen. and oxygen thru lines 4 and 5 respectively. Further control ofcombustion is afforded by regulation of the admission of steam fromlines 6 and I to either or both of the hydrogen and oxygen supply linesas required. The gases evolved are withdrawn near the top of the furnace2, thru line 8, and a portion of these gases is carried thru line 9, tothe purifying column l0, containing a solid chemical reagent for removalof fluorine compounds and carbon dioxide, where the fluorine compoundsand other undesirable compounds are separated. The gas from columnlllpwhich is principally steam, is carried by line i l, to supply theblower l-2, which delivers the steam to line l3. Line I4, delivers steamfrom line l3 to near the bottom of furnace 2 and line l5 supplies steamto lines 6 and I as required for the control of the combustion of thehydrogen and oxygen. Conveyor l6, withdraws the treated phosphate rockfrom furnace 2.

One example of the operation of my process is given for the treatment ofTennessee brown phosphate rock. The natural rock is crushed and screenedto remove portions larger than 4 mesh in diameter or fine phosphate rockis agglomerated and screened to remove portions larger than 4 mesh indiameter for use as charging stock. This charge is fed into the top ofthe furnace where it is heated by the steam and other vapors ascendingfrom the high temperature zone below. This preheated rock graduallypasses to the high temperature zone where a temperature of 1300 to 1400"C. is maintained by the combustion of hydrogen with oxygen. The rate offlow of the rock thru the high temperature zone is controlled to permitsuflicient time for the removal of most of the fluorine contained in therock. The rock continues in its course to the bottom of the furnacewhile being cooled by a countercurrent flow of vapors consistingprincipally of steam and obtained by the purification of a portion ofthe gases which have been withdrawn from near the top of the furnace.

It is evident that there, are numerous factors which will influenceconditions for the most'satisfactory operation of my process, the actuallimits of which cannot be established except by a detailed study of eachset 01' raw materials-and finished products involved.

The hydrogen and oxygen may be conveniently and economically produced bythe electrolysis of sodium hydroxide solution with the direct production.of the correct volume ratios for combustion.

Any other suitable means for the production ofeither or both of thesegases may be utilized. The fine, granular phosphate rock or the fine,granular agglomerated phosphate rock is not required to be limited toany particular size but from the practical standpointpreferably'contalus little material finer'than mesh or coarser than 4mesh. It has been found that the presence of silica is essential for themost effective defluorination of phosphate rock. The amount of silicanaturally accompanying the phosphate is usually present in sufilcientquantities but in the event of a deficiency this maybemade up by theappropriate addition of silica or silicabearing material. The furnace ispreferably designed so that the gases passing upward from the hightemperature zone of 1300 to 1400 C. are cooled to a temperature of to C.by the descending rock, and so that the heated rock from the highertemperature zone is cooled a temperature oi 100 to 150 C. by theascending steam which has been admitted near the bottom of the furnace.

All of the gases withdrawn from the top of the furnace may be purifiedif it is considered desirable to recover the material that wouldotherwise be called impurities in the steam or if it is considereddesirable to use the steam in excess of that required by the process.The gas purification will ordinarily consist in the removal of thefluorine compounds by dry purification only but other constituents ofthe gas, such as carbon dioxide, may be removed as well if desired.

I claim: a

1. Continuous process of treating phosphate rock to render it availablefor plant food which comprises heating a mass of fine, granularphosphate rock by contact with the product of combustion of a mixture ofhydrogen and oxygen, controlling the temperature of the product of ofother gaseous materials.

combustion of the mixture oi hydrogen and oxygen by the admission ofsteam to maintain the phosphate rock Just below its sintering point,treating a portion of the gases evolved for the removal of combinedfluorine and carbon dioxide 5 to produce a substantially purified steam,and

contacting the mass oiheated phosphate rock countercurrently with thepurified steam.

2. Continuous process of treating phosphate rock to render it availablefor plant food which 10 comprises heating a mass of .fine, granularphosphate rock, to a temperature just belowthe sintering point of thephosphate rock, by contact with the product of combustion of a mixtureof hydrogen and omen, in the substantial absence 15 of other gaseousmaterials, treating a portion of the gases evolved for the removal ofcombined fluorine and carbon dioxide to produce a substantially purifiedsteam, and contacting the mass of heated phosphate rock countercurrent-20 ly with the purified steam.

3. Continuous process of treating phosphate rock to render it availablefor plant food which comprises heating a mass of fine, granular phos-.phate rock, to a temperature just below the sin- 25 tering point of thephosphate rock, by contact with the product of combustion of a mixtureof hydrogen and oxygen, in the substantial absence of other gaseousmaterials, and contacting the mass of heated phosphate rockcountercurrently 30 with steam.

4. Continuous process of treating phosphate rock to render it availablefor plant food which comprises heating amass of line, granular phosphaterock, to a temperature just below the sin- 3.? tering point of thephosphate rock, by contact with the product of combustion 'of a mixtureof hydrogen and oxygen, in'the substantial absence -HARRY A. CU'R'I'IS..40

